REVIEW — TH E NATURAL HISTORY OF SOUTH DEVON. 289 
organized creation being ordained to counterbalance each other, 
as the laws of dependence pervade the world of living beings 
in all its parts, any determination or regulation such as the one 
mentioned — the diminution of numbers, and deterioration in size 
and qualities of individuals — provided it were general, and ob- 
served in all classes and species, need not excite surprise. 
The secondary causes , according to our author, are “ tem- 
perature, food , situation , and the hostility of other species.” 
“ The influence of these appears to be very considerable ; and 
though we cannot be altogether warranted in attributing the 
above-named circumstances of diminution in number and dete- 
rioration in size, &c. to these causes, however plausible it might 
seem to do so, they are undoubtedly the agents that cause dete- 
rioration generally.” 
The author then illustrates these remarks by examples from 
South Devon, and other places. Of the first of these secondary 
causes or influences ranking as laws of geographic distribution 
of animals which he mentions is climate, a term which includes 
a consideration of temperature, of seasons, of winds usually 
prevalent, of the dryness or humidity of the air, of rain, drought, 
continued cold or heat, &c. It deserves notice, that the pre- 
sence of mountains, rivers, seas, barren spots, the quality of soil, 
the degree of cultivation, and the clearness or cloudiness of the 
sky, have all some influence in forming the climate, and, in con- 
sequence, the fauna of a country. Secondary laws seem to act 
and re-act largely on each other, so that no one of them appears 
to have a separate or unmixed influence on animal distribution. 
Thus the animal part of the creation is almost entirely dependent, 
on the vegetable world, whilst the vegetable kingdom, in its 
turn, is dependent on inorganic matter, temperature, &c. 
Taking Dartmoor as an example, he says, “ Its central districts 
present to the eye a series of hills of great size, covered with de- 
tached blocks of granite. On the summit of many of these hills 
are found swamps, and even pools, of great depth, and between 
them streams pass on for future coalescence ; and where the sur- 
face is level for a sufficient space, the drainings of the country 
rest and form morasses and lakes. 
“The flora of this wild district consists, with but few excep- 
tions, of the lower tribes, such as mosses, ferns, lichens, &c., 
and of such plants as are peculiar to marshes and other collec- 
tions of water. The soil cannot possibly support many of the 
higher orders ; but the beauty, variety and luxuriance of those 
vegetable forms which mantle the rude blocks of granite, spring 
from the spongy soil of the bogs and marshes, or, maintaining 
their existence in the body of the current attached to some fixed 
VOL. xiv. p p 
